1. Field of the invention
The present invention relates to a magnetic material for high frequencies and, more particularly, to a magnetic ceramic composition for high frequency circuit elements designed for use in the microwave and millimeter wave frequency ranges.
2. Description of the Prior Art
As a magnetic material for high frequencies, there have been used materials such as Mn-Mg ferrites, Ni-Zn ferrites, YIG ferrites, lithium ferrites these materials are highly advantage in that they have high saturation magnetization (4.pi.Ms) ranging from 500 to 4000 gauss. Among them, lithium ferrite has the greatest potential for use in the production of highly stable circuit elements such as isolators and circulators. This is because lithium ferrite, has a large saturation magnetization of about 3700 gauss, a high Curie temperature (Tc) of about 650.degree. C., and a small temperature coefficient of saturation magnetization at room temperature.
However, lithium ferrite has some disadvantages such that it measures large losses in the ferromagnetic resonance line width (.DELTA.H) and the dielectric loss tangent (tan .delta.e) as compared with the other ferrite materials used in the construction of microwave and millimeter wave frequencies. For example, pure lithium ferrite, Li.sub.0.5 Fe.sub.2.5 O.sub.4, has a large value of the ferromagnetic resonance line width (.DELTA.H) of more than 500 Oersted and a dielectric loss tangent (tan .delta.e) of more than 0.01 at 10 GHz. These properties make it impossible to use as a magnetic material for practical circuit elements for microwave and millimeter wave frequencies.